Chul-Min Chon - Academia.edu (original) (raw)

Papers by Chul-Min Chon

Research paper thumbnail of 열추적자를 이용한 지하수-하천수 혼합대 연구

Research paper thumbnail of Geochemical Characteristics and Heavy Metal Distribution in Selected Volcanic Ash Soils in Jeju Island

Journal of the Korean Society of Mineral and Energy Resources Engineers, 2006

Research paper thumbnail of Setting Behavior and Phase Evolution on Heat Treatment of Metakaolin-Based Geopolymers Containing Calcium Hydroxide

Materials, 2021

The setting behavior of geopolymers is affected by the type of source materials, alkali activator... more The setting behavior of geopolymers is affected by the type of source materials, alkali activators, mix formulations, and curing conditions. Calcium hydroxide is known to be an effective additive to shorten the setting period of geopolymers. However, there is still room for improvement in the understanding of the effect of calcium hydroxide on the setting and phase evolution of geopolymers. In this study, the setting behavior and phase evolution of geopolymer containing calcium hydroxide were investigated by XRD analysis. The setting time of the geopolymer was inconsistently shortened as the amount of calcium hydroxide increased. A low calcium hydroxide dose of up to 2% of the total mix weight could contribute to the enhancement of compressive strength of geopolymers besides a fast-setting effect. The C-S-H gel is rapidly precipitated at the early stage of reaction in geopolymers containing high calcium hydroxide with some of the calcium hydroxide remaining intact. The ex-situ high-...

Research paper thumbnail of Adsorption of Arsenic (iii) and Heavy Metals by Nano-Composite of Fe and Mn Oxides

Research paper thumbnail of Potential of IGCC slag as an alkali activated material

Integrated gasification combined cycle (IGCC) is a next generation energy production technology t... more Integrated gasification combined cycle (IGCC) is a next generation energy production technology that converts coal into syngas with enhanced power generation efficiency and environmental performance. IGCC produces coal gasification slag as the solid by-product. Recycling of IGCC slag is still in the early stages, but the recycling process has been around the cement and concrete industry. We calculated the reactive Si/Al ratio of IGCC slag which is generated from a pilot plant in South Korea, and evaluated the potential of it as an alkali-activated material. Samples which were activated with the combined activator of sodium silicate solution and caustic soda had an average compressive strength of 4.5 MPa, showing swelling on the top free surface. Expansion of the alkali-activated slag was possibly caused by free CaO and MgO in the slag. While the samples that were activated with the combined activator of sodium aluminate and caustic soda had an average compressive strength of 10 MPa....

Research paper thumbnail of Washing of Petroleum and Arsenic Contaminated Soil with Ultrasound and Alkali Phosphate Solution

Soil washing of fine textured soil has been a challenging remedial strategy due to its low remedi... more Soil washing of fine textured soil has been a challenging remedial strategy due to its low remediation efficiency. We adapted ultrasound and dispersion solution to increase the remediation efficiency of the soil washing. The ultrasound and dispersion agent may enhance the dispersion of the aggregate into individual particles and may enhance release of contaminants from the aggregate. We collected the arsenic (As) contaminated silt loam soil from a smelting site, spiked with 1% of diesel and incubated for 6 months. We tested the dispersion rate and the release of diesel with the incubated soil at various pH and concentrations of orthophosphate, pyrophosphate and hexametaphosphate with or without the ultrasound of 28 kHz and 400 W. The As concentrations of coarse (> medium silt) and fine (<medium slit) fractions were also determined after the washing. The dispersion rate and diesel release increased with increasing phosphate concentration and pH of the solution. The application ...

Research paper thumbnail of Volcanic Origin Potential Acid Sulfate Soil Material

Research paper thumbnail of Effect of geopolymer composition and curing conditions on efflorescence in lightweight porous geopolymers

Research paper thumbnail of Bacterial Community Structure Analysis for a Heavy Metal Contaminated Mine Impacted Soil Remediation Process

Research paper thumbnail of Compressive Strength Properties of Geopolymers from Pond Ash and Possibility of Utilization as Synthetic Basalt

Journal of the Korean Ceramic Society, 2019

Pond ash is a mixture of mostly coarser fly ash and bottom ash. The recycling rate of pond ash is... more Pond ash is a mixture of mostly coarser fly ash and bottom ash. The recycling rate of pond ash is low because pond ash is mixed with seawater and deposited in ponds. The pond ash is also subjected to natural weathering over a period of time. In this study, we investigated whether pond ash can be used as a raw material of geopolymers, without any purification process or through a minimal purification process. In addition, we investigated whether synthetic basalt made by adding foaming agent to geopolymer or casting it into a mold can show the surface of the natural basalt as it is. The highest 7-day compressive strength in geopolymers from pond ash without purification process was 26 MPa. The highest 7-day compressive strength in geopolymers from pond ash with impurities removed through dry sieve analysis was found to improve to 80 MPa. On the other hand, synthetic basalt made with geopolymer was shown to be more advantageous aesthetically when produced by casting it in a silicone mold rather than by adding a foaming agent. Non-purified pond ash can be made into geopolymers having low strength. Pond ash purified by sieving can, without use of an aggregate, be made into geopolymer having high-strength. Also, it is possible to produce synthetic basalt with the same appearance as natural basalt and sufficient strength for commercialization. This process will contribute to the mass consumption and recycling of pond ash.

Research paper thumbnail of Enhanced oxidation resistance of NaBH4-treated mackinawite (FeS): Application to Cr(VI) and As(III) removal

Chemical Engineering Journal, 2018

Sulfide minerals are important in immobilizing toxic contaminants in reducing environments. Iron ... more Sulfide minerals are important in immobilizing toxic contaminants in reducing environments. Iron sulfide (FeS) is ubiquitous in anoxic conditions and is a good scavenger of various organic and redox sensitive contaminants and heavy metals. Despite its contaminant removal capabilities, FeS has not been used as a practical adsorbent in contaminant removal due to its rapid oxidation under atmospheric conditions. To increase its applicability, we developed a method of modifying FeS by the addition of NaBH 4 to form the less oxygen-sensitive NaBH 4-FeS. We conducted oxidation tests using laboratory batch testing and real-time synchrotron X-ray absorption spectroscopy (XAS). The Fe K-edge XAS results showed that the oxidation rate of NaBH 4-FeS was eight times slower than that of unmodified FeS while maintaining comparable contaminant removal capacities for Cr(VI) and As(III). The results of mechanistic density functional theory (DFT) calculations demonstrated that the oxidation of FeS occurred through electron transfer from sulfur of FeS to an oxidizing agent of oxygen, and that the hydride ion provided by NaBH 4 retarded electron transfer from the FeS surface.

Research paper thumbnail of Treating Dissolved Iron in Acid Mine Drainage Using Slow-Release Hydrogen Peroxide

Geological Society of America Abstracts with Programs, 2018

Research paper thumbnail of Influence of Fine Aggregate Properties on Unhardened Geopolymer Concrete

Journal of the Korean Recycled Construction Resources Institute, 2016

It is possible that aggregates add on to geopolymer based fly ash to mix mortar and concrete like... more It is possible that aggregates add on to geopolymer based fly ash to mix mortar and concrete like cement. This is necessary to evaluate mineral composition, particle shape, surface, size distribution, density and absorption ratio for fine aggregates due to few detailed research to examine influence of fine aggregates properties on unhardened geopolymer concrete. In this research, used two different fine aggregates, Jumunjin sand(having quartz, mica, feldspar, pyroxene in mineral composition, more than 96% of total size between-0.60 and +0.30mm, angular shape and rough surface) and ISO sand(having almost all quartz in mineral composition, more than 51% size between-1.40 and +0.60mm, simultaneously varied size distribution, spherical shape and smooth surface). After an experimental result of the varied ratio of Si/Al=1.0-4.1 geopolymer paste, mix proportion respectively applied Si/Al=1.5 having the highest compressive strength to mortar and Si/Al=3.5 having the highest consistency to concrete. Geopolymer mortar by mixing with Jumunjin and ISO sand in varied range of 20-50wt.% showed flow size increase between 69.5 and 112.0mm, between 70.5 and 126.0mm respectively. Geopolymer concrete at an addition of 77wt.% of total aggregates ratio showed that average compressive strength was 32MPa and the consistency was favorable to molding. Since ISO sand observing varied size distribution, spherical shape, smooth surface, low absorption ratio resulted in advantageous properties on consistency of geopolymer, geopolymer concrete can be suitable for using the fine aggregates similar to ISO sand.

Research paper thumbnail of Calcite precipitation by ureolytic plant (Canavalia ensiformis) extracts as effective biomaterials

KSCE Journal of Civil Engineering, 2014

An extract of the indigenous plant jack bean (Canavalia ensiformis) was used to produce calcite, ... more An extract of the indigenous plant jack bean (Canavalia ensiformis) was used to produce calcite, an effective biomaterial. The formation of calcite using this extract was compared, under stable conditions, to that using commercially available purified urease. Xray diffraction and scanning electron microscopy were employed to elucidate the mechanism of calcite formation from the crude plant extracts. The results revealed that urease in the jack bean crude extracts catalyzed the hydrolysis of urea in liquid-state cultures. The procedure described herein is a simple and useful method of calcite mineral precipitation that does not require cultivation of microorganisms or further purification of crude extracts. This study suggests that crude extracts of Canavalia ensiformis have the potential to be used in place of purified forms of urease during remediation of cracks and to increase the strength of materials.

Research paper thumbnail of 하동화력발전소 비산재의 입도크기와 미연탄소 함량이 지오폴리머의 압축강도에 미치는 영향

Korean Journal of Materials Research, 2013

Fly ash is one of the aluminosilicate sources used for the synthesis of geopolymers. The particle... more Fly ash is one of the aluminosilicate sources used for the synthesis of geopolymers. The particle size distribution of fly ash and the content of unburned carbon residue are known to affect the compressive strength of geopolymers. In this study, the effects of particle size and unburned carbon content of fly ash on the compressive strength of geopolymers have been studied over a compositional range in geopolymer gels. Unburned carbon was effectively separated in the −46 µm fraction using an air classifier and the fixed carbon content declined from 3.04 wt% to 0.06 wt%. The mean particle size (d 50) decreased from 22.17 µm to 10.79 µm. Size separation of fly ash by air classification resulted in reduced particle size and carbon residue content with a collateral increase in reactivity with alkali activators. Geopolymers produced from carbon-free ash, which was separated by air classification, developed up to 50 % higher compressive strength compared to geopolymers synthesized from raw ash. It was presumed that porous carbon particles hinder geopolymerization by trapping vitreous spheres in the pores of carbon particles and allowing them to remain intact in spite of alkaline attack. The microstructure of the geopolymers did not vary considerably with compressive strength, but the highest connectivity of the geopolymer gel network was achieved when the Si/Al ratio of the geopolymer gel was 5.0.

Research paper thumbnail of The origin of emission color of reduced and oxidized ZnGa2O4 phosphors

Solid State Communications, 2004

ABSTRACT The Ga–O octahedral structure of the reduced and the oxidized ZnGa2O4 phosphors was inve... more ABSTRACT The Ga–O octahedral structure of the reduced and the oxidized ZnGa2O4 phosphors was investigated using Reitveld refinement. The correlation between the structural change and the changing emission color was studied. The emission peak shifts to shorter wavelength because of the more contribution of a variation of ligand charge than that of bond length to crystal field. The blueshift behavior of the reduced ZnGa2O4 was also observed in Ge4+-doped ZnGa2O4. In addition, Li+ ions doping in ZnGa2O4 generate extra oxygen ions, and Li+-doped ZnGa2O4 shows the same emission color as the oxidized ZnGa2O4.

Research paper thumbnail of Structural changes and oxidation of ferroan phlogopite with increasing temperature: in situ neutron powder diffraction and Fourier transform infrared spectroscopy

Physics and Chemistry of Minerals, 2006

The thermal response of the natural ferroan phlogopite-1M, K 2 (Mg 4.46 Fe 0.83 Al 0. 34 Ti 0.22)... more The thermal response of the natural ferroan phlogopite-1M, K 2 (Mg 4.46 Fe 0.83 Al 0. 34 Ti 0.22)(Si 5.51 Al 2. 49)O 20 [OH 3.59 F 0.41 ] from Quebec, Canada, was studied with an in situ neutron powder diffraction. The in situ temperature conditions were set up at À263, 25, 100°C and thereafter at a 100°C intervals up to 900°C. The crystal structure was refined by the Rietveld method (R p =2.35-2.78%, R wp =3.01-3.52%). The orientation of the O-H vector of the sample was determined by the refinement of the diffraction pattern. With increasing temperature, the angle of the OH bond to the (001) plane decreased from 87.3 to 72.5°. At room temperature, a = 5.13 Å , b = 9.20 Å , c = 10.21 Å , b= 100.06°a nd V(volume) = 491.69 Å 3. The expansion rate of the unit cell dimensions varied discontinuously with a break at 500°C. The shape of the M-octahedron underwent some significant changes such as flattening at 500°C. At temperatures above 500°C, the octahedral thickness and mean distance was decreased, while the octahedral flattening angle increased. Those results were attributed to the Fe oxidation and dehydroxylation processes. The dehydroxylation mechanism of the ferroan phlogopite was studied by the Fourier transform infrared spectroscopy (FTIR) after heated at temperatures ranging from 25 to 800°C with an electric furnace in a vacuum. In the OH stretching region, the intensity of the OH band associated with Fe 2+ (N B-band) begun to decrease outstandingly at 500°C. The changes of the IR spectra confirmed that dehydroxylation was closely related to the oxidation in the vacuum of the ferrous iron in the M-octahedron. The decrease in the angle of the OH bond to the (001) plane, with increasing temperature, might be related to the imbalance of charge in the M-octahedra due to Fe oxidation.

Research paper thumbnail of Infiltration pattern in a regolith–fractured bedrock profile: field observation of a dye stain pattern

Hydrological Processes, 2006

We examined the infiltration pattern of water in a regolith–bedrock profile consisting of two ove... more We examined the infiltration pattern of water in a regolith–bedrock profile consisting of two overburdens (OB1 and OB2), a buried rice paddy soil (PS), two texturally distinctive weathered materials (WM1 and WM2) and a fractured sedimentary rock (BR), using a Brilliant Blue FCF dye ...

Research paper thumbnail of The role of clay minerals in the reduction of nitrate in groundwater by zero-valent iron

Chemosphere, 2010

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright

Research paper thumbnail of A novel chitosan/clay/magnetite composite for adsorption of Cu(II) and As(V)

Chemical Engineering Journal, 2012

Research paper thumbnail of 열추적자를 이용한 지하수-하천수 혼합대 연구

Research paper thumbnail of Geochemical Characteristics and Heavy Metal Distribution in Selected Volcanic Ash Soils in Jeju Island

Journal of the Korean Society of Mineral and Energy Resources Engineers, 2006

Research paper thumbnail of Setting Behavior and Phase Evolution on Heat Treatment of Metakaolin-Based Geopolymers Containing Calcium Hydroxide

Materials, 2021

The setting behavior of geopolymers is affected by the type of source materials, alkali activator... more The setting behavior of geopolymers is affected by the type of source materials, alkali activators, mix formulations, and curing conditions. Calcium hydroxide is known to be an effective additive to shorten the setting period of geopolymers. However, there is still room for improvement in the understanding of the effect of calcium hydroxide on the setting and phase evolution of geopolymers. In this study, the setting behavior and phase evolution of geopolymer containing calcium hydroxide were investigated by XRD analysis. The setting time of the geopolymer was inconsistently shortened as the amount of calcium hydroxide increased. A low calcium hydroxide dose of up to 2% of the total mix weight could contribute to the enhancement of compressive strength of geopolymers besides a fast-setting effect. The C-S-H gel is rapidly precipitated at the early stage of reaction in geopolymers containing high calcium hydroxide with some of the calcium hydroxide remaining intact. The ex-situ high-...

Research paper thumbnail of Adsorption of Arsenic (iii) and Heavy Metals by Nano-Composite of Fe and Mn Oxides

Research paper thumbnail of Potential of IGCC slag as an alkali activated material

Integrated gasification combined cycle (IGCC) is a next generation energy production technology t... more Integrated gasification combined cycle (IGCC) is a next generation energy production technology that converts coal into syngas with enhanced power generation efficiency and environmental performance. IGCC produces coal gasification slag as the solid by-product. Recycling of IGCC slag is still in the early stages, but the recycling process has been around the cement and concrete industry. We calculated the reactive Si/Al ratio of IGCC slag which is generated from a pilot plant in South Korea, and evaluated the potential of it as an alkali-activated material. Samples which were activated with the combined activator of sodium silicate solution and caustic soda had an average compressive strength of 4.5 MPa, showing swelling on the top free surface. Expansion of the alkali-activated slag was possibly caused by free CaO and MgO in the slag. While the samples that were activated with the combined activator of sodium aluminate and caustic soda had an average compressive strength of 10 MPa....

Research paper thumbnail of Washing of Petroleum and Arsenic Contaminated Soil with Ultrasound and Alkali Phosphate Solution

Soil washing of fine textured soil has been a challenging remedial strategy due to its low remedi... more Soil washing of fine textured soil has been a challenging remedial strategy due to its low remediation efficiency. We adapted ultrasound and dispersion solution to increase the remediation efficiency of the soil washing. The ultrasound and dispersion agent may enhance the dispersion of the aggregate into individual particles and may enhance release of contaminants from the aggregate. We collected the arsenic (As) contaminated silt loam soil from a smelting site, spiked with 1% of diesel and incubated for 6 months. We tested the dispersion rate and the release of diesel with the incubated soil at various pH and concentrations of orthophosphate, pyrophosphate and hexametaphosphate with or without the ultrasound of 28 kHz and 400 W. The As concentrations of coarse (> medium silt) and fine (<medium slit) fractions were also determined after the washing. The dispersion rate and diesel release increased with increasing phosphate concentration and pH of the solution. The application ...

Research paper thumbnail of Volcanic Origin Potential Acid Sulfate Soil Material

Research paper thumbnail of Effect of geopolymer composition and curing conditions on efflorescence in lightweight porous geopolymers

Research paper thumbnail of Bacterial Community Structure Analysis for a Heavy Metal Contaminated Mine Impacted Soil Remediation Process

Research paper thumbnail of Compressive Strength Properties of Geopolymers from Pond Ash and Possibility of Utilization as Synthetic Basalt

Journal of the Korean Ceramic Society, 2019

Pond ash is a mixture of mostly coarser fly ash and bottom ash. The recycling rate of pond ash is... more Pond ash is a mixture of mostly coarser fly ash and bottom ash. The recycling rate of pond ash is low because pond ash is mixed with seawater and deposited in ponds. The pond ash is also subjected to natural weathering over a period of time. In this study, we investigated whether pond ash can be used as a raw material of geopolymers, without any purification process or through a minimal purification process. In addition, we investigated whether synthetic basalt made by adding foaming agent to geopolymer or casting it into a mold can show the surface of the natural basalt as it is. The highest 7-day compressive strength in geopolymers from pond ash without purification process was 26 MPa. The highest 7-day compressive strength in geopolymers from pond ash with impurities removed through dry sieve analysis was found to improve to 80 MPa. On the other hand, synthetic basalt made with geopolymer was shown to be more advantageous aesthetically when produced by casting it in a silicone mold rather than by adding a foaming agent. Non-purified pond ash can be made into geopolymers having low strength. Pond ash purified by sieving can, without use of an aggregate, be made into geopolymer having high-strength. Also, it is possible to produce synthetic basalt with the same appearance as natural basalt and sufficient strength for commercialization. This process will contribute to the mass consumption and recycling of pond ash.

Research paper thumbnail of Enhanced oxidation resistance of NaBH4-treated mackinawite (FeS): Application to Cr(VI) and As(III) removal

Chemical Engineering Journal, 2018

Sulfide minerals are important in immobilizing toxic contaminants in reducing environments. Iron ... more Sulfide minerals are important in immobilizing toxic contaminants in reducing environments. Iron sulfide (FeS) is ubiquitous in anoxic conditions and is a good scavenger of various organic and redox sensitive contaminants and heavy metals. Despite its contaminant removal capabilities, FeS has not been used as a practical adsorbent in contaminant removal due to its rapid oxidation under atmospheric conditions. To increase its applicability, we developed a method of modifying FeS by the addition of NaBH 4 to form the less oxygen-sensitive NaBH 4-FeS. We conducted oxidation tests using laboratory batch testing and real-time synchrotron X-ray absorption spectroscopy (XAS). The Fe K-edge XAS results showed that the oxidation rate of NaBH 4-FeS was eight times slower than that of unmodified FeS while maintaining comparable contaminant removal capacities for Cr(VI) and As(III). The results of mechanistic density functional theory (DFT) calculations demonstrated that the oxidation of FeS occurred through electron transfer from sulfur of FeS to an oxidizing agent of oxygen, and that the hydride ion provided by NaBH 4 retarded electron transfer from the FeS surface.

Research paper thumbnail of Treating Dissolved Iron in Acid Mine Drainage Using Slow-Release Hydrogen Peroxide

Geological Society of America Abstracts with Programs, 2018

Research paper thumbnail of Influence of Fine Aggregate Properties on Unhardened Geopolymer Concrete

Journal of the Korean Recycled Construction Resources Institute, 2016

It is possible that aggregates add on to geopolymer based fly ash to mix mortar and concrete like... more It is possible that aggregates add on to geopolymer based fly ash to mix mortar and concrete like cement. This is necessary to evaluate mineral composition, particle shape, surface, size distribution, density and absorption ratio for fine aggregates due to few detailed research to examine influence of fine aggregates properties on unhardened geopolymer concrete. In this research, used two different fine aggregates, Jumunjin sand(having quartz, mica, feldspar, pyroxene in mineral composition, more than 96% of total size between-0.60 and +0.30mm, angular shape and rough surface) and ISO sand(having almost all quartz in mineral composition, more than 51% size between-1.40 and +0.60mm, simultaneously varied size distribution, spherical shape and smooth surface). After an experimental result of the varied ratio of Si/Al=1.0-4.1 geopolymer paste, mix proportion respectively applied Si/Al=1.5 having the highest compressive strength to mortar and Si/Al=3.5 having the highest consistency to concrete. Geopolymer mortar by mixing with Jumunjin and ISO sand in varied range of 20-50wt.% showed flow size increase between 69.5 and 112.0mm, between 70.5 and 126.0mm respectively. Geopolymer concrete at an addition of 77wt.% of total aggregates ratio showed that average compressive strength was 32MPa and the consistency was favorable to molding. Since ISO sand observing varied size distribution, spherical shape, smooth surface, low absorption ratio resulted in advantageous properties on consistency of geopolymer, geopolymer concrete can be suitable for using the fine aggregates similar to ISO sand.

Research paper thumbnail of Calcite precipitation by ureolytic plant (Canavalia ensiformis) extracts as effective biomaterials

KSCE Journal of Civil Engineering, 2014

An extract of the indigenous plant jack bean (Canavalia ensiformis) was used to produce calcite, ... more An extract of the indigenous plant jack bean (Canavalia ensiformis) was used to produce calcite, an effective biomaterial. The formation of calcite using this extract was compared, under stable conditions, to that using commercially available purified urease. Xray diffraction and scanning electron microscopy were employed to elucidate the mechanism of calcite formation from the crude plant extracts. The results revealed that urease in the jack bean crude extracts catalyzed the hydrolysis of urea in liquid-state cultures. The procedure described herein is a simple and useful method of calcite mineral precipitation that does not require cultivation of microorganisms or further purification of crude extracts. This study suggests that crude extracts of Canavalia ensiformis have the potential to be used in place of purified forms of urease during remediation of cracks and to increase the strength of materials.

Research paper thumbnail of 하동화력발전소 비산재의 입도크기와 미연탄소 함량이 지오폴리머의 압축강도에 미치는 영향

Korean Journal of Materials Research, 2013

Fly ash is one of the aluminosilicate sources used for the synthesis of geopolymers. The particle... more Fly ash is one of the aluminosilicate sources used for the synthesis of geopolymers. The particle size distribution of fly ash and the content of unburned carbon residue are known to affect the compressive strength of geopolymers. In this study, the effects of particle size and unburned carbon content of fly ash on the compressive strength of geopolymers have been studied over a compositional range in geopolymer gels. Unburned carbon was effectively separated in the −46 µm fraction using an air classifier and the fixed carbon content declined from 3.04 wt% to 0.06 wt%. The mean particle size (d 50) decreased from 22.17 µm to 10.79 µm. Size separation of fly ash by air classification resulted in reduced particle size and carbon residue content with a collateral increase in reactivity with alkali activators. Geopolymers produced from carbon-free ash, which was separated by air classification, developed up to 50 % higher compressive strength compared to geopolymers synthesized from raw ash. It was presumed that porous carbon particles hinder geopolymerization by trapping vitreous spheres in the pores of carbon particles and allowing them to remain intact in spite of alkaline attack. The microstructure of the geopolymers did not vary considerably with compressive strength, but the highest connectivity of the geopolymer gel network was achieved when the Si/Al ratio of the geopolymer gel was 5.0.

Research paper thumbnail of The origin of emission color of reduced and oxidized ZnGa2O4 phosphors

Solid State Communications, 2004

ABSTRACT The Ga–O octahedral structure of the reduced and the oxidized ZnGa2O4 phosphors was inve... more ABSTRACT The Ga–O octahedral structure of the reduced and the oxidized ZnGa2O4 phosphors was investigated using Reitveld refinement. The correlation between the structural change and the changing emission color was studied. The emission peak shifts to shorter wavelength because of the more contribution of a variation of ligand charge than that of bond length to crystal field. The blueshift behavior of the reduced ZnGa2O4 was also observed in Ge4+-doped ZnGa2O4. In addition, Li+ ions doping in ZnGa2O4 generate extra oxygen ions, and Li+-doped ZnGa2O4 shows the same emission color as the oxidized ZnGa2O4.

Research paper thumbnail of Structural changes and oxidation of ferroan phlogopite with increasing temperature: in situ neutron powder diffraction and Fourier transform infrared spectroscopy

Physics and Chemistry of Minerals, 2006

The thermal response of the natural ferroan phlogopite-1M, K 2 (Mg 4.46 Fe 0.83 Al 0. 34 Ti 0.22)... more The thermal response of the natural ferroan phlogopite-1M, K 2 (Mg 4.46 Fe 0.83 Al 0. 34 Ti 0.22)(Si 5.51 Al 2. 49)O 20 [OH 3.59 F 0.41 ] from Quebec, Canada, was studied with an in situ neutron powder diffraction. The in situ temperature conditions were set up at À263, 25, 100°C and thereafter at a 100°C intervals up to 900°C. The crystal structure was refined by the Rietveld method (R p =2.35-2.78%, R wp =3.01-3.52%). The orientation of the O-H vector of the sample was determined by the refinement of the diffraction pattern. With increasing temperature, the angle of the OH bond to the (001) plane decreased from 87.3 to 72.5°. At room temperature, a = 5.13 Å , b = 9.20 Å , c = 10.21 Å , b= 100.06°a nd V(volume) = 491.69 Å 3. The expansion rate of the unit cell dimensions varied discontinuously with a break at 500°C. The shape of the M-octahedron underwent some significant changes such as flattening at 500°C. At temperatures above 500°C, the octahedral thickness and mean distance was decreased, while the octahedral flattening angle increased. Those results were attributed to the Fe oxidation and dehydroxylation processes. The dehydroxylation mechanism of the ferroan phlogopite was studied by the Fourier transform infrared spectroscopy (FTIR) after heated at temperatures ranging from 25 to 800°C with an electric furnace in a vacuum. In the OH stretching region, the intensity of the OH band associated with Fe 2+ (N B-band) begun to decrease outstandingly at 500°C. The changes of the IR spectra confirmed that dehydroxylation was closely related to the oxidation in the vacuum of the ferrous iron in the M-octahedron. The decrease in the angle of the OH bond to the (001) plane, with increasing temperature, might be related to the imbalance of charge in the M-octahedra due to Fe oxidation.

Research paper thumbnail of Infiltration pattern in a regolith–fractured bedrock profile: field observation of a dye stain pattern

Hydrological Processes, 2006

We examined the infiltration pattern of water in a regolith–bedrock profile consisting of two ove... more We examined the infiltration pattern of water in a regolith–bedrock profile consisting of two overburdens (OB1 and OB2), a buried rice paddy soil (PS), two texturally distinctive weathered materials (WM1 and WM2) and a fractured sedimentary rock (BR), using a Brilliant Blue FCF dye ...

Research paper thumbnail of The role of clay minerals in the reduction of nitrate in groundwater by zero-valent iron

Chemosphere, 2010

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright

Research paper thumbnail of A novel chitosan/clay/magnetite composite for adsorption of Cu(II) and As(V)

Chemical Engineering Journal, 2012